Build one for 10EUR. If you can't - ask in electric repair shop, even with that payment it will cost you more or less 20EUR (it takes 10-15 minutes to solder the parts). 3 themes before, there was a link for a collection of zapper circuits.
Aside - Ravo Zapper looks good, I am not sure if you need so much options. It is not proved that multi frequency zappers works better than single freq (30kHz or 2.5kHz or whatever). But looking at the characteristics, it seems a real hi-tech product, engineered and produced carefully (compared to some pricy self-made bizarre semi-devices it is far superior).
The sweeping zapper just with hand holds looks acceptable. The one which uses box of multimeter is too cheap and non-serious for me (subjective evaluation).
Why you don't try this: http://cgi.ebay.com/Micro-Mini-Hulda-Clark-Zapper_W0QQitemZ350068008236QQihZ0...
I never seen this in real, but on picture looks good :) And if it doesn't work for you, at least the loss will be less (just 20USD).
Btw, for 300EUR I would suggest to take SCENAR, depends what you are targeting to do with it. Do some research about it.